1. Field of the Invention
The present invention relates to rendering devices and, more specifically, to a rendering device for generating display image data representing maps on a display.
2. Description of the Background Art
The above type of rendering device has often been incorporated in a navigation device. EP Patent No. 1,024,467, Japanese Patent Laid-Open Publication No. 2000-276609, and EP Patent No. 777,206 each disclose such a navigation device with the rendering device incorporated therein. In this Description of the Background Art section, those navigation devices are respectively referred to as a first, second, and third navigation devices in that order. These navigation devices are each described below for a rendering process executed therein.
In a rendering process, in the first navigation device, a distance from the current vehicle position to any object to be rendered which is located in a close range of the vehicle position is calculated. If the calculated distance is equal to a predetermined threshold value or smaller, the object is three-dimensionally rendered. On the other hand, if the calculated distance exceeds a predetermined threshold value, the object is two-dimensionally rendered, thereby resulting in a lower viewability as compared with the object which is three-dimensionally rendered. Herein, the object denotes an element of a display map, e.g., a building.
In the second navigation device, a distance from the current vehicle position to any object to be rendered which is located in a close range of the vehicle position is also calculated. Based on the calculated distance, a color density of the object to be rendered is determined. Herein, the object denotes a polygon representing a road in a display map.
In the third navigation device, a route search is first completed for guiding the vehicle. When the vehicle comes within a predetermined range of each intersection on the found route, any objects (typically landmarks) in the vicinity of the road leading to the intersection are to be rendered on a map.
The problem with the third navigation device, however, is that, as in the first and second navigation devices, changing the manner of rendering the objects based on their distance from the vehicle position to the target object often fails to result in maps meeting the users"" demands and needs.
Referring to FIGS. 22A to 22C, the problem is described in more detail. FIG. 22A shows an intersection C1 to which first to third roads W1 to W3 are connected. Presumably, the vehicle is allowed to go through the intersection C1 from the first road W1 to the second road W2, but the vehicle is prohibited to go in the opposite direction, i.e., from the second road W2 to the first road W1. Under such a presumption, there is a xe2x80x9cNo Entryxe2x80x9d sign TS1 provided in the vicinity of the intersection C1. As shown in FIG. 22B, the road sign TS1 shows a message on a main plane TS11 facing the second road W2, but as shown in FIG. 22C, its opposite plane TS12 facing the first road W1 shows no message.
When the vehicle approaches the intersection C1 coming from the direction of the second road W2, the first and second navigation devices display a map as shown in FIG. 22B. With such a map, the user in the vehicle will see the plane TS11.
On the other hand, if the vehicle approaches the intersection C1 coming from the direction of the first road W1, displayed on the first and second navigation devices is a map as shown in FIG. 22C. In this displayed map, the plane TS12 shows no message of xe2x80x9cNo Entryxe2x80x9d, and thus there is no need to include the road sign TS1 as long as the user sees the object from the first road W1 side. Even so, the first and second navigation devices both fully and clearly render the plane TS12 of the road sign TS1 as an object. As a result, the road sign TS1 blocks the user""s view in the displayed map for the area therebehind, which is a part of the driving area in which the user wants to see rather than the plane TS12 of the road sign TS1 which has no beneficial use in this case. This proves that changing the manner of rendering objects based on the calculated distance as by the first and second navigation devices is not an ideal answer for generating maps which meet users"" demands and needs, and thus is not considered driver friendly.
The third navigation device bears the same problem as described above referring to FIGS. 22A to 22C, because objects on roads in the direction to which a user travels are explicitly rendered thereby.
Therefore, an objective of the present invention is to provide rendering devices capable of generating display image data adequately in order to represent maps which are considered driver friendly, that is, those meeting users"" demands and needs.
The present invention has the following features to attain the above objective.
A first aspect of the present invention is directed to a rendering device for generating display image data which represents a map to be displayed on a display. The rendering device comprises a first reception section for externally receiving directional object data having a plurality of planes each facing a different direction. The directional object data includes direction information specifying in which directions the planes are each facing. The rendering device further comprises a rendering section for rendering, based on a positional relationship between a user""s current position and the direction information specifying in which directions the planes.are each facing, the planes of the directional object in each different manner to generate the display image data. According to the present invention, the user""s current position changes the manner of rendering the directional objects, whereby the resulting display image data can represent maps meeting the user""s demands and needs.